Liquid detergents, particularly for automatic dishwashing machines, have become increasingly popular. For such formulations, active materials which are unstable in an aqueous environment or in the presence of a bleaching agent are required, for example, nonionic surfactants are generally preferred to control foaming during the wash cycle and to reduce spotting and filming during the rinse cycle. However, many nonionic surfactants, especially those based on ethylene oxide/propylene oxide react readily with sodium hypochlorite. Many detergent formulators use either aqueous sodium hypochlorite or unencapsulated solid chloride forms and thus most nonionic surfactants are not compatible with the bleaching agent, especially in liquid formulations.
Attempts have been made to improve the compatibility of nonionics, especially alkoxylated nonionics with chlorine bleach, by "capping" the terminal hydroxyl group as described in U.S. Pat. Nos. 4,859,358 (Gabriel et al.); and 4,988,456 (Takahashi et al.).
Alternatively, the nononics and chlorine bleach may be compatibilized by separating the two into different compartments within a container and provide a means to combine them when dispensed for use or to encapsulate one of the materials.
Encapsulation of bleaches and nonionic surfactants is well known in the art as described in U.S. Pat. Nos. 3,856,699; 4,078,099; 4,126,717; 4,919,841 (Kamel et al.) and 5,200,236 (Langet al.). The described encapsulating processes include top spraying, fluidized bed and dispersion/solidification methods.
These described encapsulation processes as taught in the art may be effective in encapsulating certain actives such as a solid chlorine precursor but are not suitable for other actives such as surfactants, especially liquid nonionic surfactants. U.S. Pat. No. 5,200,236 issued to Langet al. teaches a process to encapsulate and effectively protect solid bleaches or nonionic surfactants by paraffin wax for liquid detergent application. This process is not suitable for those physical forms of actives which are not solid or easily agglomerated, such as liquids, flakes, small particles, etc. For example, a liquid active such as liquid surfactant has to be preabsorbed by more than twice its weight of solid carrier to become a solid which is then coated with wax by a fluidized bed method. This extra pregranulation process is costly and also limits the loading of a liquid active in the wax capsule.
U.S. Pat. No. 4,919,841 (Kamel) describes a dispersion and solidification process to make wax capsules. This process involves first dispersing the active core material into a molten wax at a temperature higher than the melting temperature of the wax, and then adding the active molten wax dispersion to an aqueous medium. The mixture is cooled to form the wax capsules. The described process is extremely difficult to use to encapsulate surfactants which are surface active molecules and tend to orient themselves at the oil/water interface. Poor trapping of surfactants by the wax capsule results when this process is used.
Thus, there is a need for a useful wax encapsulation process which is efficient in encapsulating solid or liquid actives for use in liquid cleaning products.